The present invention relates to a novel diamine hole transport agent, and, more particularly, to a novel diamine compound having an improved hole transport capability and a high glass transition temperature, and an organic electroluminescent device containing same.
Generally, an organic electroluminescent device has a laminated structure comprising a transparent electrode layer, a metallic electrode layer, and an organic interlayer including an organic luminescent layer arranged between the two electrodes. The organic interlayer comprising an organic luminescent layer may further include a hole transport layer sandwiched between the transparent electrode layer and the organic luminescent layer, and may still further include an electron transport layer inserted between the metallic electrode layer and the organic luminescent layer, often in a multilayer configuration to increase luminous efficiency.
Hitherto, aromatic tertiary amines such as tetraphenylbiphenyldiamine (TPD), N-phenylcarbazole, 4,4xe2x80x2-bis[N-(1-naphthyl)-N-phenylamino]biphenyl(NPB) have been used in forming a hole transport layer.
However, due to the fact that the above-mentioned compounds have low glass transition temperatures ranging from 60 to 95xc2x0 C., electroluminescent devices containing such hole transport agents have low heat stability, bad resistance to external impact, and short lifetime under hard environment.
Therefore, there has existed a need to develop a novel compound having a high glass transition temperature for use in an electroluminescent device with improved hole transport capability.
Accordingly, it is a primary object of the present invention to provide a novel compound having an improved hole transport capability and a high glass transition temperature, and an organic electroluminescent device containing same.
In accordance with one aspect of the present invention, there is provided a diamine compound of formula (I): 
wherein, Ar1 is a phenyl or biphenyl group, and Ar2 is a phenylene or 
group, Ar1 and Ar2 being optionally fused to form, together with the nitrogen atom attached thereto, substituted carbazole derivative.